1. Field of the Invention
The present invention relates to an optical information recording medium having an ink absorbing layer, in which printing can be directly made on a surface (label surface) opposed to a recording/reproducing surface of the optical information recording medium.
2. Description of the Related Technology
An optical information recording medium having a label surface, in which an ink absorbing layer is formed to enable printing to be directly made on the medium by, e.g., an ink jet printer, (i.e., the so-called printable product), has been used more extensively.
Ink absorbing layers of general printable products have mat surfaces with no gloss. Recently, however, a printable product having a high gloss has been marketed to provide a higher-quality appearance by adding a new property of gloss to the ink absorbing layer.
Further, there is known an invention in which the surface gloss of an ink absorptive resin layer of a printable optical recording medium is specified and the surface roughness of the ink absorptive resin layer is controlled to be 0.40 μm or less so that a printed image has a sharper appearance (see Japanese Unexamined Patent Application Publication No. 2002-237103).
The invention of Japanese Unexamined Patent Application Publication No. 2002-237103 takes into account the surface gloss of an ink absorptive resin layer, but it includes no particular description about a gloss level after printing of an image. Regarding high quality after printing of an image (i.e., realization of high-definition design), Japanese Unexamined Patent Application Publication No. 2002-237103 states, “By forming the outermost layer on the label surface of the optical recording medium to have a small roughness, a gloss and ink absorptivity, the optical recording medium having a glossy printable layer can be provided which enables users to optionally print a high-definition image with quality comparable to that of a photo on the medium surface by using an ink jet printer or a thermal transfer printer.” (Paragraph [0012]) Further, regarding features of such an optical recording medium, Japanese Unexamined Patent Application Publication No. 2002-237103 states, “The present invention resides in the optical recording medium featured by having, as the outermost layer, an ink absorptive resin layer with a 60° specular gloss of 30 to 150 at its surface. Also, the present invention resides in the optical recording medium featured by having, as the outermost layer, an ink absorptive resin layer with a surface roughness (Ra) of 0.40 μm or less.” (Paragraph [0013])
The marketed printable products having a high gloss include ink absorptive resin layers with a 60° specular gloss of 30 to 150 at their surfaces and a surface roughness (Ra) of 0.40 μm or less. In other words, the properties of the marketed printable products are just matched with the technical features disclosed in Japanese Unexamined Patent Application Publication No. 2002-237103.
However, when images are actually printed on those products, it often occurs that a printed area is apt to loose the gloss and a large difference in gloss is generated between the printed area and a not-printed area, thus resulting in an image finished with poor quality.
Stated another way, the product disclosed in Japanese Unexamined Patent Application Publication No. 2002-237103 and the other known gloss printable products cannot realize high-quality printing from the practical point of view.
Meanwhile, there is also known a product of the type that paper having a gloss (so-called glossy paper) can be pasted onto a label surface. Such a product realizes a glossy and high-quality image by allowing the glossy paper (image), which is printed by a printer or the like, to be pasted onto the label surface.
Thus, an improvement of printing quality has been tried by controlling a gloss level of the printable product.
Printing an image on glossy paper can realize high-quality printing with less disappearance of gloss even after the printing. However, such a method has a disadvantage in that the specific functions (optical recording and reproducing) of the optical information recording medium are seriously impeded in some cases. More specifically, the medium is susceptible to wobbling in rotation due to, e.g., a misalignment of the pasted label and a deviation in weight distribution accuracy of the paper itself. Also, the medium is susceptible to warp due to deformations (such as expansion and contraction) of the label. Those undesirable events tend to cause errors during the process of recording and reproducing. Further, there is a risk that the pasted label is half or fully peeled off. In such a case, the half or fully peeled-off label may be caught in a drive unit, thus leading to damage of a disk and/or a drive.
In the situations described above, a technique capable of keeping sharpness of a printed image without loosing the gloss in appearance even after the printing is demanded in the printable product represented by the optical information recording medium in which the ink absorbing layer is directly formed on the label surface without pasting the glossy paper.